Non-A, Non-B hepatitis (NANBH) is a transmissible disease (or family of diseases) that is believed to be virally induced, and is distinguishable from other forms of virus-associated liver disease, such as those caused by hepatitis A virus (HAV), hepatitis B virus (HBV), delta hepatitis virus (HDV), cytomegalovirus (CMV) or Epstein-Barr virus (EBV). Epidemiologic evidence suggests that there may be three types of NANBH: the water-borne epidemic type; the blood or needle associated type; and the sporadically occurring (community acquired) type. However, the number of causative agents is unknown. Recently, however, a new viral species, hepatitis C virus (HCV) has been identified as the primary (if not only) cause of blood-associated NANBH (BB-NANBH). See for example, PCT WO89/046699; U.S. patent application Ser. No. 7/456,637, filed 21 Dec. 1989; and U.S. patent application Ser. No. 7/456,637, filed 21 Dec. 1989, incorporated herein by reference. Hepatitis C appears to be the major form of transfusion-associated hepatitis in a number of countries, including the United States and Japan. There is also evidence implicating HCV in induction of hepatocellular carcinoma. Thus, a need exists for an effective method for treating HCV infection: currently, there is none.
Many viruses, including adenoviruses, baculoviruses, comoviruses, picornaviruses, retroviruses, and togaviruses, rely on specific, virally-encoded proteases for processing polypeptides from their initial translated form into mature, active proteins. In the case of picornaviruses, all of the viral proteins are believed to arise from cleavage of a single polyprotein (B. D. Korant, CRC Crit Rev Biotech (1988)8:149-57).
S. Pichuantes et al, in "Viral Proteinases As Targets For Chemotherapy" (Cold Spring Harbor Laboratory Press, 1989) pp. 215-22, disclosed expression of a viral protease found in HIV-1. The HIV protease was obtained in the form of a fusion protein, by fusing DNA encoding an HIV protease precursor to DNA encoding human superoxide dismutase (hSOD), and expressing the product in E. coli. Transformed cells expressed products of 36 and 10 kDa (corresponding to the hSOD-protease fusion protein and the protease alone), suggesting that the protease was expressed in a form capable of autocatalytic proteolysis.
T. J. McQuade et al, Science (1990) 247:454-56 disclosed preparation of a peptide mimic capable of specifically inhibiting the HIV-1 protease. In HIV, the protease is believed responsible for cleavage of the initial p55 gag precursor transcript into the core structural proteins (p17, p24, p8, and p7). Adding 1 .mu.M inhibitor to HIV-infected peripheral blood lymphocytes in culture reduced the concentration of processed HIV p24 by about 70%. Viral maturation and levels of infectious virus were reduced by the protease inhibitor.